Infrared Measurements of Jet-Stream Cirrus

Abstract

An experimental investigation into the radiative characteristics of jet-stream cirrus was undertaken by using AFCRL's research instrumented U-2 aircraft. Radiation measurements in the 8–13 μ window region along with aerial photography were made by flying the aircraft at various altitudes above and through the cirrus regimes. The results of this investigation are described. The window radiation data obtained over and in jet-stream cirrus give little information as to the absolute cloud height or temperature. The results of direct observations from the U-2 aircraft suggets a very wide range of values of emission and transmission for cirrus cloud regimes in the 8–13 μ window region. The blackbody assumption in this region as it pertains to cirrus clouds must be abandoned. Deviations of radiometric from ambient cirrus temperatures range from 0–68K. These temperature deviations cause errors of 0–30,000 ft in estimating the height of the cirrus tops. It is possible to improve cirrus height and temperature estimates by categorizing the radiation measurements and assigning an effective cirrus emission-transmission factor.